1. Field of the Invention.
The present invention relates generally to low temperature well cementing compositions, and more particularly, to hydraulic cement compositions which have improved resistance to deterioration as a result of freeze-thaw cycling and methods of cementing therewith.
2. Description of the Prior Art.
A variety of hydraulic cement compositions have been developed for performing cementing operations in subterranean earth formations penetrated by a wellbore. For example, hydraulic cement compositions are commonly used in primary cementing operations in oil and gas wells whereby pipe, such as casing and liners, are cemented in well bores. In the usual primary cementing operation, a hydraulic cement composition is introduced into a well bore by way of the pipe to be cemented therein and displaced into the annular space between the pipe and the surrounding formation. The cement composition is allowed to set into a solid mass or sheath, whereby the annular space is sealed and the pipe is bonded to the formation. In other cementing operations, i.e., secondary cementing or remedial operations, a hydraulic cement composition is placed in cracks or voids in the sheath or formation and allowed to set therein so that fluid tight seals result.
When primary and secondary cementing operations are performed in low temperature earth formations, i.e., formations which are frozen or periodically subjected to freezing, various problems are encountered. For example, when conventional hydraulic cement compositions are placed in low temperature subterranean formations, long periods of set time are required to enable the compositions to develop sufficient compressive strengths to permit resumption of drilling or completion operations. In addition, conventional cement compositions exhibit high heats of hydration which can cause surrounding frozen formations to melt to thereby prevent proper bonding of the cement compositions to the formations as well as promoting destabilization of the formation. Furthermore, conventional cement compositions utilized in frozen formations have also frozen prior to setting to thereby prevent setting and/or the development of sufficient compressive strengths. In addition to the above, prior cement compositions have failed due to deterioration in compressive strength of set cements caused by exposure of the set cement to freeze-thaw cycling. Freeze-thaw cycling is the expression used to refer to cyclic variations in temperature about and below the freezing point of water.
Special hydraulic cement compositions and methods for carrying out well cementing operations at low temperatures have been developed and utilized heretofore. For example, related U.S. Pat. Nos. 3,891,454 and 3,937,282 issued on Jun. 24, 1975 and Feb. 10, 1976, respectively, disclose cement compositions and methods for carrying out well cementing operations in low temperature earth formations. While such cement compositions and methods have been used successfully, problems have still been encountered in wells in which freeze-thaw cycling occurs. That is, the special low temperature cement compositions have low freezing points, rapidly set and develop strength at low temperatures, and have low heats of hydration. However, when the set cement compositions are subjected to freeze-thaw cycling, relatively rapid cracking and crumbling of the cement takes place whereby the cement loses its compressive strength as well as its bonding and sealing ability.
Thus, there is a need for improved hydraulic cement compositions and methods for cementing wells drilled through low temperature earth formations whereby the set cement has resistance to deterioration as a result of freeze-thaw cycling.